As an improvement over the spray painting of articles such as automobile bodies, boats and household appliances, a new kind of paint-coated sheet material (also called paint-coated film) has been developed to provide protective and decorative finishes. The new material comprises a flexible, stretchable, thermoplastic carrier film which has a protective and decorative paint layer of uniform thickness and appearance on one side, and, optionally, an adhesive layer on the other side. It can also have other layers such as a tie or bonding layer between the paint layer and the carrier film. In a preferred embodiment, a transparent topcoat covers the paint layer to provide an attractive basecoat-clearcoat appearance. Such a sheet material is disclosed in the copending patent application of Reafler, Ser. No. 116,426, filed Nov. 3, 1987, now abandoned, and in the corresponding European Patent Office application WO89/04257 published May 18, 1989. These and the other cited applications and patents are incorporated herein by reference.
In the Reafler sheet materials, the carrier film has heat-softening and tensile elongation properties which adapt it to use in thermoforming. The various layers have compatible heat-softening and tensile elongation properties. As a result, the sheet material can undergo substantial elongation during thermoforming without crazing or delamination of the layers.
In use, the paint-coated film is stretched and bonded by thermoforming to a substrate such as a three-dimensional automobile panel. The procedure of thermoforming can be substantially as described in the patent to Short et al, U.S. Pat. No. 4,769,100 wherein the film is heated and then drawn by vacuum into bonding contact with the substrate. Notwithstanding its excellent thermoforming characteristics, this high quality sheet material can develop surface roughness after it has been bonded to a substrate such as the exterior of an automobile when it is exposed to excessive heat for extended periods of time.
A vacuum forming process for adhesively bonding a thermoplastic sheet to an interior automobile panel is described in U.S. Pat. No. 3,551,232 issued Dec. 29, 1970. The objective of this patent is to overcome the problems of bubbling and blistering of the thermoplastic sheet that tend to occur in the vacuum forming process. It achieves this by use of an adhesive containing an inert particulate filler which minimizes the entrapment of air. The use of an adhesive composition that contains granular particles is not believed to be conducive to obtaining a smooth surface. Furthermore, in the case of exterior automobile panels, it is necessary not only to prevent air entrapment during thermoforming, but also to avoid later development of surface roughness.
U.S. Pat. Nos. 4,059,466; 4,059,714 and 4,156,754 are directed to methods of making and using hot melt foamed adhesives which are said to have an increased bonding strength and to be useful for packaging when a quick setting time of the adhesive is designed.
U.S. Pat. No. 3,523,846 relates to the production of porous, self-adhesive tapes by converting a visco-elastic self-adhesive mass into a fine vesicular condition by evaporation and transferring a layer of the mass to a porous base under pressure.
U.S. Pat. No. 3,380,866 to T. O. Glinter, discloses the use of a polyester adhesive containing a blowing agent for reducing stresses that develop during the bonding of reinforced resin components.
While the above-cited patents relate to the preparation and use of liquid adhesives, none of them offer any suggestion that the use of a foamed adhesive for the bonding of a flexible, stretchable paint-coated film, to a substrate which is subject to high-temperature weathering conditions will prevent roughening or texturing of the bonded film.